1. Field of the Invention
The present invention relates to rotary position sensors used for detecting rotation angles of various devices or for detecting the amount of depression of a pedal, such as an accelerator pedal, on the basis of a rotation angle of a rotating member which moves in conjunction with the pedal. More specifically, the present invention relates to a magnetic rotary position sensor which requires a waterproof, explosion-protective structure for an electrical circuit component installed therein.
2. Description of the Related Art
In a typical magnetic rotary position sensor, a magnet is attached to a rotating member, and a magnetic field of the magnet is applied to a magnetoelectric transducer. The magnetoelectric transducer detects the magnetic field of the magnet which changes in accordance with the rotation of the magnet, and the sensor outputs an electrical signal representing the rotation angle of the rotating member. Thus, it is not necessary to store an electrical circuit component which is constructed by mounting electronic parts, such as the magnetoelectric transducer, on a circuit board and a rotating mechanism which is rotated by a detection object in the same space. Therefore, a structure for protecting the electrical circuit component from external water and combustible gas can be obtained relatively easily.
More specifically, it is not easy and involves high costs to completely seal the rotating mechanism, which is mechanically connected to the detection object, and it is difficult to maintain the reliability of the seal for a long time. Accordingly, in optical and resistive sensors, in which the space for storing the rotating mechanism and the space for storing the electrical circuit component must be continuous to each other, it is not practicable to obtain a waterproof, explosion-protective structure for the electrical circuit component with low cost or to maintain the reliability of the waterproof, explosion-protective structure. On the contrary, in magnetic sensors, the detection accuracy is not affected even when the space for storing the rotating mechanism and the space for storing the electrical circuit component are not continuous to each other, and only the electrical circuit component, for which the waterproof and explosion-protective structure is necessary, must be sealed. Thus, magnetic sensors are advantageous in view of reliability improvement and cost reduction.
With respect to such magnetic rotary position sensors, a sensor in which a seal block which contains the electrical circuit component and which is sealed with resin is combined with the rotating mechanism and a housing has been proposed. In such a known sensor, the seal block is constructed in advance as an electrical circuit component unit having a waterproof, explosion-protective structure, and the housing in which the rotating mechanism including the magnet is rotatably retained is attached to the seal block. Therefore, even when external water or combustible gas enters the rotating mechanism, the electrical circuit component enclosed in the seal block can be reliably protected.
In the above-described known rotary position sensor, it is not technically difficult to form the seal block which encloses the electrical circuit component. However, since a resin block, which defines the size of the seal block, must completely surround the electrical circuit component and be provided with an engaging member for being engaged with the housing on the exterior of the resin block, there is a limit to the reduction in the overall size, including thickness. Accordingly, a large amount of resin must be used and a complicated forming process must be performed for obtaining the seal block. In addition, the product assembly process cannot be performed until a complicated sealing process is completed. Therefore, the above-described known sensor has problems in that it cannot be manufactured with sufficient yield and the cost of the product increases.
In view of the above-described situation, an object of the present invention is to provide a magnetic rotary position sensor in which a waterproof, explosion-protective structure for an electrical circuit component can be easily established and which can be manufactured with high yield and at low cost.
In order to attain the above-described object, a rotary position sensor according to the present invention includes a cylindrical housing having a partition wall in the interior thereof; a rotating member which is stored in a space between a first open end of the housing and the partition wall in such a manner that the rotating member can rotate; a magnet which is provided on the rotating member at a position close to the partition wall and which generates a magnetic field which extends beyond the partition wall toward a second open end of the housing; a first cover which closes the first open end in such a manner that a shaft portion of the rotating member projects outward from the housing; an electrical circuit component which includes a magnetoelectric transducer and which is stored in a space between the second open end of the housing and the partition wall in such a manner that the magnetoelectric transducer is placed at a position close to the partition wall; and a second cover which closes the second open end so as to seal the electrical circuit component. The magnetic field of the magnet which is applied to the magnetoelectric transducer changes in accordance with the rotation of the rotating member, and the electrical circuit component outputs an electrical signal corresponding to a rotation angle of the rotating member.
In the rotary position sensor which is constructed as described above, since the interior of the housing is divided into two spaces by the partition wall, a rotating mechanism (the rotating member, the magnet, etc.) and the electrical circuit component can be stored in different spaces and be completely separated from each other by the partition wall. Therefore, a waterproof, explosion-protective structure for the electrical circuit component can be easily established by simply sealing a gap between the second cover and the housing with a small amount of resin, an O-ring, etc., and it is not necessary to perform a complex sealing process. In addition, since the rotating mechanism and the electrical circuit component can be installed in different spaces without causing them to interfere with each other, an assembly process can be easily performed and the yield can be easily increased. Accordingly, an inexpensive magnetic rotary position sensor having high reliability can be provided.
Preferably, the partition wall of the housing is provided with a support member receiver which supports the rotating member in such a manner that the rotating member can rotate, so that the number of components can be reduced and the overall thickness can also be reduced. In this case, preferably, magnetic poles of the magnet may be arranged such that opposite poles face each other across a rotational center of the rotating member; a support projection is provided on the bottom surface of the rotating member at the rotational center of the rotating member, the support projection being in contact with the support member receiver and being pivotally supported by the support member receiver; and the magnetoelectric transducer is a giant magnetoresistive (GMR) element which is disposed at a position such that the giant magnetoresistive element faces the support projection across the partition wall. In this case, the rotating member is pivotally supported by the support member receiver with the support projection therebetween, so that even when lateral pressure is applied, the rotating member can be prevented from being displaced in the lateral direction and only tilts around a pivot center. Even when the rotating member tilts, the magnetic field detected by the giant magnetoresistive element is affected only slightly. Accordingly, the rotation angle of the rotating member can be detected by the giant magnetoresistive element with high accuracy even when lateral pressure is applied, and the detection accuracy can be improved.
In addition, when the support projection is composed of a metal and the support member receiver is composed of a resin, abrasion of the support projection can be prevented and an end portion of the support projection can be substantially in point contact with the support member receiver for a long time. Accordingly, the pivot center of the rotating member can be stably maintained at the same position. In addition, preferably, the partition wall projects toward the first open end so that a recess is provided as viewed from the second open end, and the giant magnetoresistive element is disposed in the recess. In such a case, the giant magnetoresistive element can be easily positioned in a region where the magnetic force is strong and the detection accuracy can be further improved.